The field of the invention is catalysts used in the synthetic production of higher fatty acids and the present invention is particularly concerned with the recovery of cobalt catalysts used in the production.
The state of the art of the production of fatty acids or the corresponding fatty acid derivatives by reacting olefins with carbon monoxide and an appropriate compound containing a replaceable hydrogen atom such as water or alkanol in the presence of a catalyst containing a metal of Group VIII of the Periodic Table of elements and possibly also a promoter may be ascertained by reference to J. FALBE, "Synthesen mit Kohlenmonoxid", Springer published, Berlin, Heidelberg, New York, 1967 and U.S. Pat. Nos. 3,507,891 and 3,856,832, the disclosures of which are incorporated herein.
As a preferred embodiment of the reaction of olefins with carbon monoxide and a compound containing a replaceable hydrogen atom, where the reaction is called hydrocarboxylation, the reaction takes place in the presence of cobalt catalysts. An especially preferred embodiment consists in additionally using a promoter, in particular pyridine or a non-ortho-substituted alkylpyridine.
This homogeneously catalyzed reaction suffers from the substantial disadvantage that the relatively costly cobalt must be recovered from the reaction mixture in a form which permits its re-use as a catalyst.
The process disclosed in U.S. Pat. No. 3,856,832 solves this problem by carrying out the olefin reaction with carbon monoxide in the presence of an excess of alkanol and paraffin, or paraffin is added after the reaction is completed. In this manner a two-phase mixture is formed. The lower phase consists predominantly of alkanol and promoter and contains a maximum of about 97% of the cobalt used as catalyst. The upper paraffinic phase consists essentially of non-reacted olefin and reaction products.
The lower phase containing the catalyst still in active form, is used in the reaction. However, the advantage so obtained is more than negated by the loss of about 3% of the cobalt used. A hydrocarboxylation method can only be considered economically satisfactory when the cobalt in the paraffinic phase is also recovered. In view of the excess of alkanol and the addition of paraffin required for the method of U.S. Pat. No. 3,856,832, such reprocessing is very costly.
Another process for recovering the cobalt catalyst is described in U.S. Pat. No. 3,507,891. The method is characterized by recovering the cobalt together with the sump product from the reprocessing by distillation of the reaction mixture.
When the reaction mixture is subjected to an oxidizing treatment prior to reprocessing by distillation, for instance oxidizing with air, the catalyst is recovered in a form from which the active catalyst species is produced again only under the conditions of the hydrocarboxylation. It would appear that an oxidizing treatment of the reaction mixture can be dispensed with only when alkylpyridines are used as promoters. Thermostable complexes would be expected to form, and retain their activity, in the presence of these promoters under the conditions of distillation.
While the process of U.S. Pat. No. 3,507,891 does offer a way to widely recover the cobalt used, it nevertheless fails to provide, just as the method of U.S. patent application Ser. No. 125,482 fails to provide, a way for separating high boiling-point substances and other interfering contaminants which inevitably are formed as by-products in the hydrocarboxylation.